Slide-fastener stringers generally comprise a pair of slide fastener or stringer halves, each of which is formed with a flexible support tape, e.g. of fabric, along a coupling edge over which is provided a row of coupling members, teeth or heads adapted to interdigitate with the coupling members of an opposing row upon movement or a slider along the stringer.
While the row of coupling members can be formed from a continuous thermoplastic strand in the form of a coil or a meander, or even may be molded in a bar shape with a multiplicity of protuberances forming the spaced-apart heads, the row of coupling members can be provided as discrete molded thermoplastic members in a given equispaced relationship.
These members can be individually clamped and preferably thermally bonded to the support tape, or can be provided in the form of a coupling element which can consist of the row of coupling members molded onto and thereby affixed to a core or cord of thermoplastic or textile material which can extend along the strand and which can be engaged in a weave or net of the fabric tape to mount the coupling members along the edge. In such cases, as well the coupling members may be bonded to the tape and may lie on one side thereof or may straddle the edge of the tape.
Such coupling elements can be produced in a continuous manner and incorporated in the slide-fastener stringer substantially continuously so that the stringer is produced in a continuous manner and lengths can be cut therefrom to form the usual slide fasteners.
Sliders can be applied to the slide-fastener and are adapted to ride along the rows of coupling members, being guided by flanks or formations thereof, while endstop members can be provided individually at each end of each row or to both rows, depending upon whether the slide fastener is of the separable or nonseparable type. In use, the tape of each slide-fastener half is affixed, e.g. by stitching, to one side of an opening in an article which can be closed by movement of the slider.
It is known to form substantially continuous rows of coupling members by molding them from thermoplastic synthetic resin onto textile strands such as the cords or cores mentioned previously with a forming wheel whose periphery is provided with form beds or cavities into which the synthetic resin material is injected or extruded through openings in a continuous band which is fed to the periphery of the wheel and lies thereagainst during the introduction of the synthetic resin and the cooling or setting thereof. The band can then be drawn away from the periphery of the wheel to extract the row of coupling members from the mold cavities and enable this row to be separated, in turn, from the wheel.
A synthetic resin extruder, usually of the worm type, has an outlet, mouth or nozzle which presses against this latter band to force the synthetic resin material through the successive openings thereof into the underlying mold cavities.
One or more textile strands, cores or cords can be fed to the mold cavities between the wheel and the band, either of which can have formations receiving this strand to enable the connecting members to be molded around the strand.
The coupling members can be applied directly to the support tape or can be subjected to further shaping, i.e. bending around the edge of the tape, and are free from projections on the side of each coupling member confronting the tape and from undercuts.
Such projections or undercuts are desirable for a number of reasons. For example, the projections can pass through openings in the tape for engagement with an opposite shank and/or for stable positioning of the coupling members on the tape. When single shank coupling members are provided, these projections may merely fit into gaps in a tape for stable positioning whereas they may also be bonded to yarns of the tape if this mode of attachment is desired. The properties and undercuts can guide a slider.
When they are constructed as double-shank members, the bight from which the two shanks extend to straddle the edge of the tape, forms the coupling head.
Thus it has been recognized heretofore that it is desirable to provide projections, undercuts or other formations on the coupling member in the region of the tape so as to establish a form-locking or form-fitting connection therewith.
In earlier systems, these formations were produced by subjecting the coupling members, usually after withdrawal from the wheel, to deformation treatment. The products molded in the cavities on the wheel, therefore, can be intermediates in the production of the final coupling shape.
With double-strand coupling members, two spaced-apart parallel core strands can be employed so that the coupling members, before being bent to straddle the edge of the tape, constitute "rungs" of the "ladder" formed by the row.
Naturally, when the band with preshaped openings is fed to the periphery of the forming wheel which has correspondingly spaced mold cavities, the operation of these elements must be synchronized so that each mold cavity registers with a respective opening.
A system of the type described having molding beds or cavities in the forming wheel and openings in the forming band, which completely define the shape of the coupling members or intermediates, is disclosed in German patent document (Open Application-Offenlegungsschrift) DE-OS No. 25 37 059. Neither the finished coupling members nor intermediates (which require further forming such as bending to straddle the tape) can be provided with protuberances, ridges or projections which can overhang the slide fastener plane or can be associated with undercuts, can be provided without additional forming steps upon removal of the members from the mold cavities. Such formations are desirable, especially in the case of single-shank coupling members, to form guide surfaces for the slider.
The term "shank" is used to distinguish between the edge of the tape and is shaped to form the coupling head, and the portion which extends away from the head and serves to secure the coupling member to the tape. This latter portion is turned away from the head and is generally elongated.